Method and apparatus for electrically heating articles



1929. H. E. NORMAN 1,734,913

METHOD AND APPARATUS FOR ELECTRICALLY HEATING ARTICLES Fil y 1927 -2Sheets-Sheet 1 IN VEN TOR.

A TTORNEYS.

m 6%W1 W s ja 5 Nov. 5, 1929. NORMAN 1,734,913

METHOD AND APPARATUS FOR ELECTRICALLY HEATING ARTICLES File July 192 2Sheets-Sheet 2 INVENTOR.

ATTORNEYS.

Patented Nov. 5, 1929 UNHTED STATES PATENT "OFFICE HORACE E. NORMAN, OFSPRINGFIELD, MASSACHUSETTS, ASSIGNOR TO NATIONAL EQUIPMENT COMPANY, OFSPRINGFIELD, MASSACHUSETTS, A CORPORATION OF MASSACHUSETTS METHOD ANDAPPARATUS FOR ELECTRIOALLY HEATING ARTICLES Application filed July 14,

This invention relates'to a method and ap- .paratus for electricallyheating metals, of the class in which the resistance increases with'thetemperature thereof.

This method and apparatus has been developed particularly for use inelectrically heating articles preparatory to forging but obviously thecharacter of the operation, which ensues after the articles have beenheated, is largely immaterial. The invention will be disclosed herein,by way of illustrative example, as adapted to heat one end of an articlepreparatory to an upsetting or heading operation.

The heating is effected by placing the article, or that portion thereofwhich is to be heated, between contacting electrodes in the usual or anysuitable way. One of these electrodes has a larger area of contact withthe article than the other and is usually cooled, so that heating isinitiated adjacent the other electrode, being the point of highestresist- The latter electrode usually engages the article at the endwhich is to be upset and the heating therefore starts at such end andprogresses inwardly. VVha-t is needed for proper heating of the articlefor the upsetting operation is a so-called soaking heat which penetratesinto the article a substantial distance from the end engaged by the lastnamed electrode. That is, a certain length of the article, measured fromone end thereof, mustbe heated with substantial uniformity. This result,however, is not readily obtained. The article heats first at point ofhighest resistance, namely, at one end, and as this end gets hotter itsresistance increases and thereby heats still more rapidly, making worseconditions which are already bad as tending to produce non-uniformheating. The action, if allowed to continue, will cause burning ofthearticle at one end before the rest of the portion of the article whichrequires heating is properly heated.

To overcome this tendency to heat the article nonuniformly, in the caseof machines having a manually operable electrode, the operator willwithdraw the electrode from contact with the hot end of the articleInomentarily, allowing the latter to 0001 some- 1927. Serial No.205,728.

what at such end and allowing the heat to All end of the article hascooled somewhat and its resistance has thereby been lowered. The

electrode may be removed and reapplied several times during the heatingof one article. In the case of machines wherein the electrodes areapplied to the article by automatic mecha'nism, the above scheme is notfeasible and the method then resorted to is to apply a relatively lowvoltage to the article for a relatively long time. The voltage can be sochosen as to avoid burning of the hot end of the article but at adistinct sacrifice of time. The very reason for the provision of theautomatic machine is to save all the time possible so that productioncan be boosted to a maximum. Consequently, it is most important, if notvitally necessary, to secure proper heating of the work in the shortestpossible time.

The problem, to the solution of which this invention is directed, is theelectrical heating of metals of the class described, properly andwithout burning, in a much shorter time than has been possible with anyof the former methods of which I am aware.

My invention offers as a solution of this problem, and has for itsobject, the cutting down of the voltage impressed on the article to beheated after the heating has progressed to a certain stage. This is doneto offset the rise in voltage which I have found occurs as a consequenceof the heating of the article, for reasons which I shall hereinafterexplain in detail.

This rise in voltage is what-causes the burning of the end of the blank.It also explains T the use of relatively low initial voltages which arepurposely chosen so low'that they will not rise high enough tocauseburning. However, I have found that if I ofiset the rise in voltage, Ican use higher initial voltages and heat the Work properly and Withoutburning in less than half the time which would otherwise be required. I

The stage in the heating of the article at which the voltage is cut downmay be deter mined in various ways. The operator, by watching theheating of the work, may judge the time at which the change is to beeffected and may manually effect the change. The change may also beautomatically effected by any suitable means which will respond to arise in voltage across the terminals of the article to be heated. Boththese methods and exemplary apparatus, by means of which the methods maybe practiced, will be disclosed herein, but it is within the province ofthis invention to determine the time when the change in voltage shouldbe made by any other suitable means,tl1e essential feature being areduction in voltage at the proper time to compensate for the rise involtage which necessarily follows as the article is heated.

These and other objects will appear in the following descriptions and bepointed out in the appended claims.

The invention will be disclosed with ref erence to the accompanyingdrawings, in which z- Fig. 1 is a diagrammatical view of one apparatusby which the method may be practiced, arranged for manual control; and

Fig. 2 is a similar view of another apparatus by which the method may bepracticed under automatic control.

Referring first to Fig. 1, (1 represents the article to be heated andfor the upsetting operation it is necessary to include only a cer tainportion, such as w, in circuit between two electrodes 6 and e. Theelectrode 6, as shown, contacts with one end face 7" of the articlewhile the electrode 6 contacts with part of the side of the article andat a distance from said end. The electrode 6 may, and often does,consist of more than one part and the manner in which this and the otherelectrode engage the work may be varied as desired,that shown beingpurely exemplary.

The electrodes 6 and e are connected, usually by heavy copper leads Zand 7/ to the secondary s of a suitable step-down heating transformer,the core of which is designated a and the primary p. The latter issupplied from an auto-transformer t, which is connected by wires 5 and 6and a double pole switch 7 to a supply line 8 of suitable voltage. Theswitch 7 is electromagnetically operated, as by the plunger 9 andsolenoid 10 which is included in circuit with a supply line 11, usuallyof lower voltage than line 8. One of the line wires 11 leads directly toone terminal of solenoid 10. The other wire 11 leads to one terminal ofa switch 12. The other terminal of the latter is connected by a wire 13to a contact 14 on the lever 15 of a regulating switch, designatedgenerally as r. This lever 15 can swing to the right or to the left ofthe illustrated position so as to move the contact 14 into engagementwith either of two fixed contacts 16 and 17. Both of the latter contactsare connected by a wire 18 to the other terminal of solenoid 10. Thelever 15 also carries a second contact, marked 19, which is insulatedfrom the contact 14 and is adanted to engage either of a pair ofcontacts 20 and 21, according to whether the lever 15 is swung to theright or to the left of the illustrated position. Contacts 20 and 21 areconnected by wires 22 and 23, respectively, to different taps 24 and 25,respectively, of the auto-transformer t,the con tact 21 being connectedto a tap of lower voltage than that to which contact 20 is connected.The contact 19 is connected by a wire 26 to one terminal of primary 7?and the other terminal of the latter is connected by a wire 27 to wire5.

The lever 15 of the regulating switch is, at the start of the heatingoperation, positioned so that contact 19 is engaged with contact 20 andso that contact 14 is engaged with contact 16. The switch 12 is theusual switch provided on the forging machine to initiate the electricheating operation. It usually is operable by movement of and with theelectrodes, being arranged to close only after the electrodes have madecontact with the work and to open only after the electrodes have beendisengaged with the work. Assuming then that lever 15 is positioned asdescribed and that the electrodes are applied to the article a, theclosing of switch 12 causes energization of solenoid 10 which in turncauses the closing of switch 7. Current then flows in the heatingcircuit and the upper end f of article (4 starts to heat. The heatingstarts here because this is the point of highest resistance in theheating circuit,-the electrodes 0 having a greater area of contact withblank 4 and beingusually also cooled. As the end f gets hot, theoperator, judging the time by the appearance of the heated article,throws lever 15 to the left, and thereby moves contact 19 out ofengagement with contact 20 and. into engagement with contact 21. This cases the primary 2) of the heating transformer to be connected to the tag25 of lower voltage whereby the voltage in the secondary or heatingcircuit will be correspondingly reduced. The above described mov'zancntof lever 15 also results in disengagement of contacts 14 and 16, wherebythe supply line switch 7 is opened, and this action preferably occursjust before the contacts 19 and 20 disengage so that there w ll be noarcing at these contacts. The switch 7 is thereafter closed again byreason of the engagement of contacts 14 and 17 and this preferablyoccurs just after contacts 19 and 21 have been engaged and for the abovereason.

Referring now to Fig. 2, the heating transformer and the heating circuitincluding its electrodes are the same as before. Also the primary p issupplied from the auto-transsupply to auto-transformertis controlled bythe electroanagnetic switch 7 which is itself controlled by switch 12from .a low'voltage circuit 11. The differences relate entirely to themanner in which the taps 24 and 25 are successively connected inthe'order named to primary p.

To effect this result, I make use of a selector switch, marked SS; acurrent relay, marked CR; and a potential relay, marked PR. The selectorswitch includes two switch -arms'30 and 31, which are connected by wires32 and 33 to the'taps 24:and 25,'respectively. Arms 30 and 31 are biasedto normally remainin open position, as shown. Arm 31 has a plunger 34for cooperation with a solenoid 35 whereby, when the latter .isenergized,

arm 31 will be swung to the .left and into Similarly,

a solenoid 38 whereby, when the latter is energized, arm 30will becaused to swing to the left vand into engagement with a contact 39.Contacts 36 and 39 are connected together and to one terminal of thesolenoid 40 of current relay CR by a wire 41. The other terminal ofsolenoid 40 is connected by a wire 42 to one terminal of primary p, theother terminal of the latter being connected by the wire 27 as before,to wire 5. The

plunger 37 differs from plunger 34 in that it carries a contact 43adapted normally to engage a fixed contact 44. The energizationofsolenoid 38, which serves to close switch '30, also serves to separatethe contacts 43,

and 44.

The current relay CR comprises, in addition to solenoid 40, a plunger 45which carries a contact 46, adapted on energization of the solenoid toengage a fixed contact 47. The potential relay PR includes a solenoid 48having a plunger 49 carrying a contact 50 which normally engages thelower contact 51 of a pair of fixed contacts, the other and uppercontact being marked 52. plunger 49 is adapted to be lifted when soleThe noid 48 is energized, whereby contact 50 is first disengaged fromcontact 51 and then engaged with contact 52. The lifting of plunger 49is, however, retarded by a dash pot, conventionally indicated at 53,whereby there is a short time interval between the disengagement ofcontacts50 and 51 and the subsequent engagementof contacts 50 and 52.Solenoid 48 is connected by a wire 54 to switch 12 and by a wire '55 tothe proper line wire 11, whereby the solenoid will be energized when andwhile switch 12 is closed. Contacts 47 and 50 are connected by a wire 56and the latter is connected to wire 54. Contacts 52 and 44 are connected'by a wire 57. Contact 43 is connected by a wire 58 to one terminal ofsolenoid '35 and the other and connect the primary 7) to the highVoltterminal of the latteris connected -by;a wire of switch 7 as before,and also energizes solenoid 38, causing arm 30 to engage contact 39agetap 24 ofauto-transformer2f. The circuit for solenoid 38 ,may betraced as follows:

from switch 12 by wire 54 to wire 56, thence by wire 56 to contact 50,which is initially engaged with contact 51, thence by wires 62 and 61'tothe-solenoid, returning by wires and 59 to the proper low voltage supplywire 11.

Current cannot flow through solenoid 35 because contacts 50 and 52 aredisengaged. Current does flow through solenoid 40 of the current relayand causes contacts 46 and .47 to engage, whereby a second path fromwire 54 to solenoid 38 is completed. This is necessary in order to keepthe solenoidenergized and switch 30 closed because the former path,which includcdcontacts 50 and 51, will be interrupted as plunger 49starts slowly upwardly under the force exerted by solenoid 48. Thelatter, of course, is energized coinciden-tally with solenoid 38. As thesolenoid 38 was energized to close switch 30, the contacts 43 and 44became separated. Consequently, when the potential relay PR eventuallycauses contact 50 to engage contact 52, the circuit which is adapted toconnect soleno'id 35 to line 11 will still :be open. Such circuit may betraced as follows: from switch 12 by wire 54 to wire 56 and contact 50,

thence from contact 52 by wire 57 to contact .105

44, thence from contact 43 by wire 58 to solonoid 35, returning by wire59 to the proper .line Wire 11. Thus, by reason of the separation ofcontacts 43-and 44, solenoid 35 will not 'be energ1zed when contacts 50and 52 engage.

article heated, as will appear, whereby the current relay may alsobe'said to respond to a rise in voltage across said terminals. Upon sucha rise in voltage and the consequent decrease in current in the heatingcircuit, there is a proportional decrease in current in the circuit ofprimary p. lVhen the current in the latter decreases below apredetermined de gree, solenoid 40 is no longer able to hold the plunger45 in raised position and it falls,

causing separation of contacts 46 and 47. It will be recalled that itwas the engagement of these contacts which was relied on to keepsolenoid 88 energized. Consequently, when they become separated,solenoid 38 will be cut off from its supply circuit and switch 30 willopen. The opening of this switch results in the engagement of contacts-13 and a l, whereby solenoid is energized and switch arm 31 is swunginto engagement with contact 36. Thus, the primary p is disconnectedfrom the high voltage tap 2d and connected, after a momentaryinterruption, to a lower voltage tap 25. The heating then continuesuntil switch 12 is opened, whereupon the supply to solenoics 35 and isinterrupted and the parts controlled thereby return to the illustratedpositions. The solenoid 38 has already been de-cnergized, wherefore theparts controlled thereby have already returned to illustrated position,as have also those controlled by current relay CR.

It has been stated that a rise in voltage across the terminals of thearticle to be heat ed occurs as the heating progresses. This rise involtage is slower than the increase in resistance of that part of thearticle being heated and not in the same proportion thereto. The rise involtage occurs for several reasons. First, the increase in resistance ofthe article being'heated causes a greater drop in voltage across itsterminals, which is one factor productive of the rise in voltagereferred to. Second, the increased resistance of the heating circuitmeans decreased current, if the secondary voltage of the heatingtransformer remains constant. This decrease in current means a lesserdrop in voltage in the leads Z and Z and thus a greater drop in voltageacross the terminals of the article being heated. Third, as the currentdecreases, the load on the heating transformer decreases as does alsothe load on the supply line 8, and these decreases in load result involtage rises. These various factors then cause a rise in voltage acrossthe terminals of the article to be heated as the heating progresses andsuch rise is accompanied by a decrease in current, which is made use ofto operate the current relay and cause a reduction in the voltageapplied to the primary ;0 and thus also to the heating circuit andarticle a.

As illustrative of a typical case and without in any sense setting up nyhard and fast limits, a voltage of 1.3 was initially applied theterminals of the article to be heated. As the heating progressed, thevoltage across said terminals rose to 1.75 volts, whereupon the voltageof the primary circuit was reduced so that the voltage across saidterminals was reduced to .9 volts. The heating was then continued andthe voltage rose to 1.2 at the end of the heating interval. The articlewas heated properly and without burning in 10 seconds. Contrasting thiswith prior practice, a low initial voltage. say .7 5 volts is used inorder that the final voltage may not rise too high and burn the work andthe heating of the work under these conditions required 25 seconds. Thiscase is given, merely as an illustrative example, to show the relativesaving in time which may be made by the use of my invention.

In the heating operation, the heating commences at the end face 7 of thearticle, being the point of greatest resistance. Heating progresses fromface f towards electrode e and the penetration of the heat to thedesired distance from said face is largely a question of time andapplied voltage. If a low enough voltage is applied across the terminalsof the article, it can be heated satisfactorily but more time is takenthan would be required if higher voltages were applied. The highervoltages, however, are likely to cause burning of the worn unlessprovisions made to prevent such action. This *ill be apparent when oneconsiders that the heat initiated at the point 7" increases theresistance at this point, resulting in the work getting hotter andhotter near one end untilitbu 5. By cutting down the voltage after thehea..-ng nears the stage at which the work would burn under formermethods, the heating effect at the hot end is diminished to compensatefor the tendency to overheat, and "he heat has time to spread along theblank by conduction before the metal can burn at point 7 My methodenables the use of higher initial voltages, which means more rapidheating, by cutting down the voltage after the heating has progressedclose to the stage at which burning might otherwise result. I believethat I am the first to conceive the method ierein set forth, and theapparatus by which the method may be practiced, and I desire to claim myinvention in the broadest possible legal manner.

lVhat I claim is:

1. The method of electrically heating articles of the class in which theresistance increases with the temperature, which consists in applying aninitial voltage to the articles and. after the voltage across thetcrminals of the article has risen to a predetermined degree, reducingthe voltage applied thereto.

2. The method of electrically heating articles of the class in which theresistance increases with the temperature. which con sists in applyingan initial voltage to the articles, allowing the voltage across theterminals of the articles to rise a predetermined degree, and thenreducing the applied voltage and continuing the operation under the lastapplied voltage.

3. In combination, an electric heating circuit including electrodes forcontacting with the article to be heated and for impressing a certaininitial voltage thereon, and compensating means responsive to a rise involtage across the terminals of said article to decrease the voltage ofsaid circuit.

4. Electric heating apparatus comprising, a heating transformer,electrodes connected to the secondary of the latter and to which thearticle to be heated is adapted to be connected, a source of E. M. F. tosupply the primary of said transformer, and means responsive to a risein voltage across the electrodes to decrease the voltage applied to saidprimary.

5. Electric heating apparatus comprising, a heating transformer,electrodes connected to the secondary of the latter and to which thearticle to be heated is adapted to be connected, an auto-transformerhaving taps to supply various voltages to said primary, a switch bymeans of which the tap of higher voltage is initially connected to saidprimary, a second switch adapted to connect a tap of lower voltage tosaid primary, and means responsive to a. rise in voltage across theterminals of said electrodes to open the first switch and close thesecond.

In testimony whereof I have affixed my signature.

HORACE E. NORMAN.

